With a 235/T-5 in a '59 truck, you will want the 3.73 or higher ratio (numerically). A 3.90 or even a 4.10 would suit that combo well with a .73 overdrive.
The reason is the lack of horsepower of the 235 compared to a V8.
The beauty of the T-5 behind a 235 is the extra and closer together shifts of the 5 speed, and the overdrive to keep it from screaming on the highway.
Every time you shift, you will be within the optimal power band of the 235. No screaming before a shift, and no lugging after the shift. 70 MPH no problem.
If GM had come out with a T-5 in 1947, there would be no such thing as a car or truck made by any other manufacturer.
